Hi Fabrizio, The issue with -O0 is that the kernels idle thread (idle_thread) on x86 is not given a stack and at -O0 the -fomit-frame-pointer optimization is not enabled (it is enabled at -O1), resulting in idle_thread attempting to use a stack. Using -O0 is therefore not recommended as you need to also (on x86 at least) add at least the -fomit-frame-pointer option to the kernel flags list. Adrian On Fri 25-May-2018 7:34 AM, Fabrizio Bertocci wrote: > Hi, > After hours of debugging I have discovered a quite nasty issue where > seL4_Wait() crash if I build the kernel without optimization (gcc option > -O0) on a pc99 tested with qemu. > > How to reproduce: Just create an endpoint (from a vka) and call > seL4_Wait(). The simplest reproducer can be obtained from the hello-2 > tutorial: > - Copy the main.c from the solution directory in the apps/hello-2/src/main.c > > - Add the following codes right after the creation of vka (TASK 5, approx > line 150): > { > printf("WAITING----------------------------------------------\n"); > seL4_Word myBadge; > vka_object_t ep_object = {0}; > error = vka_alloc_endpoint(&vka, &ep_object); > ZF_LOGF_IFERR(error, "Failed to allocate new endpoint object.\n"); > seL4_Wait(ep_object.cptr, &myBadge); > printf("---------------------------------------------- DONE!!\n"); > } > > Essentially the added code, creates an endpoint using vka and calls > seL4_Wait() on it... I expect the code to block forever since there are no > other threads that can unblock it... > > - Build it and run it with: > > make pc99_hello-2_defconfig > make > make simulate > > > Expected output: > > Booting all finished, dropped to user space > 4 untypeds of size 12 > 4 untypeds of size 13 > [...] > 6 untypeds of size 29 > WAITING---------------------------------------------- > > > - Now change the configuration using 'make menuconfig' and select: > > seL4 Kernel -> Build Options -> Compiler optimisation flag (-O2) > > and change it to -O0, save the new configuration. > > - Rebuild and run: > > make simulate > > > Now you get a kernel exception: > > [...] > 6 untypeds of size 29 > WAITING---------------------------------------------- > > ========== KERNEL EXCEPTION ========== > Vector: 0xd > ErrCode: 0xa658 > IP: 0xe0118ce5 > SP: 0xffaf7e28 > FLAGS: 0x86 > CR0: 0x8001003b > CR2: 0x0 (page-fault address) > CR3: 0x142000 (page-directory physical address) > CR4: 0x100290 > > Stack Dump: > *0xffaf7e28 == 0xe011a658 > *0xffaf7e2c == 0x0 > *0xffaf7e30 == 0x0 > *0xffaf7e34 == 0xe011a658 > *0xffaf7e38 == 0x8 > *0xffaf7e3c == 0x202 > *0xffaf7e40 == 0x0 > *0xffaf7e44 == 0x0 > *0xffaf7e48 == 0x10 > *0xffaf7e4c == 0x7 > *0xffaf7e50 == 0x0 > *0xffaf7e54 == 0x0 > *0xffaf7e58 == 0x0 > *0xffaf7e5c == 0x0 > *0xffaf7e60 == 0x0 > *0xffaf7e64 == 0x0 > *0xffaf7e68 == 0x0 > *0xffaf7e6c == 0x0 > *0xffaf7e70 == 0x0 > *0xffaf7e74 == 0x0 > > Halting... > halting... > Kernel entry via Interrupt, irq 157 > > > Version info: > > - gcc: gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-11) > - qemu: QEMU emulator version 2.0.0, Copyright (c) 2003-2008 Fabrice > Bellard > - Build environment: CentOS Linux release 7.3.1611 (Core) > > > Other info: > > - gcc 4.8.5 doesn't seem to support the 'Nehalem' x86 microarchitecture, > so I am selecting the 'Generic' microarchitecture (Toolchain Options -> X86 > microarchitecture) > - Even the tutorial 'hello-timer' fails exactly with the same exception > without any modifications if you build the kernel with -O0. > - Tested on a Beaglebone black: no problems compiling kernel with -O0 > > > Regards, > Fabrizio Bertocci > Real-Time Innovations, Inc. > > > > _______________________________________________ > Devel mailing list > Devel(a)sel4.systems > https://sel4.systems/lists/listinfo/devel >